1. Field of the Invention
The present invention relates to a technique for multiplexing and storing data in a storage system such as a RAID system.
2. Description of the Related Art
In order to improve the reliability of data storage, the data are stored in a storage system by multiplexing or typically doubling the data. In Patent Document 1, for example, there is disclosed a doubling magnetic disk device, which is connected to a host device and provided with two magnetic disk devices. This doubling magnetic disk device has a copy function and a double-line write function for doubling and storing the data in the two magnetic disk devices. According to this copy function, in response to a copy instruction from a host device, the doubling magnetic disk device reads data stored in one magnetic disk device and writes the data in the other magnetic disk device. According to this double-line write function, the doubling magnetic disk device accepts a double-line write instruction from the host device, and writes the data accepted from the host device, in parallel in both two magnetic disk devices.
[Patent Document 1] JP-A-8-263221
In order that the data may be doubled by using the aforementioned doubling magnetic disk device, the host device has to be provided with a function to issue the copy instruction or the double-line write instruction, that is, the function to control the data doubling. Naturally, resources such as the CPU or the main memory of the host device are used to control the doubling of the data or the restoration of the doubled data after a fault occurred. Since the resources of the host device are used at the data restoration after the fault, the host device may be unable to start its business quickly.